The present invention generally relates to contact lens cases.
U.S. Pat. No. 3,770,113 (Thomas) discloses a prior art contact lens storage and disinfection cup system 10. The Thomas system is illustrated in FIG. 1 of the present application, and utilizes a planar central stem 12 that engages a cap 13. The stem 12 has dome features 14 on each side of the stem 12 and hinged containment cages 16 which pivot into a closed position over the domes 14 and parallel to the planar stem 12. Subsequent commercial cup disinfection and storage systems have generally followed the same layout with only minor differences in the ribbing of the cages or the form of the dome used to receive the contact lens. This layout of the lens retaining components has withstood the test of time in part due to the efficiency in which it utilizes space available within the cup. Typically, contact lens solution makers have settled upon the use of 10 cubic centimeters (cc's) of solution within the cup for purposes of disinfection or hydration. This volume of fluid may have been driven by the geometry of the cup design disclosed in the '113 patent in order to assure that lenses were fully immersed in solution; nevertheless the 10 cc fluid volume has become standard within the lens care industry and as a consequence, subsequent lens cup designs have been driven by the need to keep contained contact lenses fully immersed in 10 cc's of fluid.
Users of these lens cases generally find it easier to deliver their lenses to the dome feature 14 instead of the cage 16. This is in part due to the tendency of the damp lens to adhere the dome surface 14 which has more surface area than the cage 16 and more closely resembles the shape of a human eyeball. Since contact lens wearers typically grasp the lens by its convex outer surface to remove it from their eye, the dome 14 provides a ready receptacle without having to change one's grasp on the lens. Contact lens wearers also show preference for larger domes and cages as opposed to smaller ones in which fingers must be more dexterous in order to place or retrieve lenses. This user preference may also be driven by an older population of contact lens wearers who may lack the dexterity of younger lens users.
Although it would prove more convenient to the user to reverse the layout of the design disclosed in the '113 patent by providing the dome 14 on the more accessible hinged member 16, this has not been commercially pursued primarily due to the inefficient utilization of space and volume presented by such a layout. Direct reversal of the cup system layout disclosed in the '113 patent would require a larger diameter cup cylinder 18 to receive the basket and stem assembly which in turn would require use of more than the standard 10 cc's of lens care solution to assure immersion of the lenses.
Another method to facilitate such reversal would be to reduce the diameter and depth of the lens cage, but this would be judged as user unfriendly by a large portion of lens wearers who find smaller lens cages difficult to use. Typically, the inner base diameter of commercial contact lens cases range from 0.70 inches to 0.80 inches, and this is what users are accustomed to using.
The contact lens case configuration 10 disclosed in the '113 patent includes a latching mechanism 20 for holding the hinged members 16 closed in order to retain the lenses. As shown in FIG. 1, the latching mechanism 20 disclosed in the '113 patent consists of latch arms 22 which are disposed on the hinged members 16 and which are configured to engage bottom surfaces 24 of the central stem member 12. Many subsequent contact lens case systems have followed the same approach and have similar latching mechanisms. However, latches such as that which is disclosed in the '113 patent have a tendency to cut lenses that are not properly aligned when the hinged member is moved into the closed, latched position.
Most contact lens are made of plastic, using a molding process. The molding process used to produce plastic lens cases is generally paced by the speed at which heat can be removed from the molten plastic resin once it has been injected into the mold. Plastic resin must be sufficiently cooled and therefore hardened to prevent distortion upon ejection or handling. Overly thick sections of plastic slow down the molding process because they require more time to cool. In some instances, thick sections can warp or suffer from surface distortions known as sink, in which the molten plastic within the thick section pulls the hardened outside skin inwards as the molten resin shrinks during cooling. Makers of contact lens storage and disinfection cases based upon the lens case configuration disclosed in the Thomas '113 patent configuration have long suffered extended molding times and sink in parts as a result of the large plastic mass necessarily contained within the back-to-back dome configuration. The optimum dome shape and size cannot be efficiently produced with this layout. Precise configurations for the dome have proven impossible to mold on a reliable basis. Attempts to create a dome form from a series of contoured ribs or place apertures within the dome's center have generally resulted in domes that fail to present sufficient surface area to hold onto the lenses placed there or domes that will not release lenses for treatment once immersed in solution. These compromised domes may not preferentially retain lenses once the stem assembly has been withdrawn from its solution bath.